Quality assurance is an important aspect of membrane module fabrication. A continuing need exists for improved nondestructive test techniques for the characterization of membranes during the fabrication process, as well as during operation of the membranes.
Ultrasonic testing has been previously used as a non-destructive test in the characterization of membrane properties. For example, longitudinal waves transmitted through a membrane from an ultrasonic source have been used as a nondestructive method of membrane testing. Behavior of the longitudinal waves within the membrane describe the physics of membrane formation, compaction, and fouling in terms of sound wave propagation within the membrane.
The reflection and transmission of elastic waves in porous media has received considerable attention because of the importance of the problem in earthquake engineering, geophysics, and soil engineering. More recently, interest has been generated in the area of applications for ultrasonic testing of porous materials such as foams. The problem has also been explored because of interest in the physics of the phenomena at a fundamental level and the possible impact on measurements in other higher density materials.
Material property characterization in elastic plates and the measurement of properties of layered plates using guided elastic waves are well-established techniques in both geophysics and non-destructive evaluation of composite materials. However, only some of these techniques are well suited for applications in materials that are as thin as microporous membranes. In addition, the issues associated with obtaining required material property values for even relatively thick porous materials present a significant challenge.